Expression node - if missing

Hello, I have been having some difficulties with the new expression node in KNIME. I want to be able to check if column ‘CANCELLED REASON’ is missing, then return values in column ‘JOB STATUS’ but if not missing, then join (JOB STATUS + CANCELLED REASON). I can only get the node to join if CANCELLED REASON is recorded. Please can someone advise? Any tips would be much appreciated. Thank you.